Relativistic MHD Simulations of jets Relativistic MHD Simulations of jets Abstract We have performed 3D RMHD simulations to investigate the stability and structure of highly relativistic MHD precessed jets with three different frequencies. As initial condition preexisting jet flow is established across the computational volume an input the precessional perturbation from the inner boundary. We show the results from simulations of a super-magnetosonic jet surrounded by a fast wind. The simulation results reveal complex pressure structure inside the RMHD jet. The structure will be produced by a combination of the helical surface and body modes excited by the precession. The jet strongly interacts with the external wind. It means significant energy loss from the jet surface. Introduction Simulation model Results Our propose We investigate a detailed analysis of the time-dependent structures of relativistic jets by using 3D relativistic MHD simulations. Relativistic jets can exhibit time-dependent curved structures with superluminally moving component (3C345 etc.) or with both superluminally moving and more slowly moving or stational components (M87, 3C120 etc.). Superluminal motions along curved trajectories can be explained by helical jet model. Helical patterns are the expected result for Kelvin- Helmholtz and Current-driven jet instabilities in relativistic flows. The numerical code 3D relativistic MHD code (Koide et al. 2000; Koide 2003; Mizuno et al. 2004) with Cartesian coordinates. The initial condition preexisting jet flow is established across the computational volume (the case in which a leading Mach disk and bow shock have passed) and leaving in a pressure balance with a low-density external wind ( j / ext =2.0). The jet flow v j =0.9165c, Lorentz factor =2.5 and external wind v ext =0.5c Adiabatic index =5/3, sound speed a ext =0.7155c, a j =0.6446c, and Alfven speed v a,ext = c, v a,j = c. The jets are super-magnetosonic flows We set vertical magnetic field (B z,j =0.1 ( c 2 ) 1/2, B z,ext =0.95*B z,j ) along the jet We input precessional perturbation with transverse velocity (v t =0.01c, 0.1c) and perturbation frequency (wR j /v j = 0.4, 0.93, 2.69) from the inner boundary Numerical region and Mesh points -3 R j < x,y < 3R j, 0 R j < z < 20R j with 90 * 90 * 300 mesh points Y. Mizuno 1,2,5 K.-I. Nishikawa 2,3, P. Hardee 3, S. Koide 4, G. J. Fishman 1 1 NASA/Marshall Space Flight Center, 2 National Space Science and Technology Center, 3 University of Alabama, 4 Department of Engineering, Toyama University, 5 NRC Research fellow 4 Summary and Future work We have performed 3D RMHD simulations to investigate the stability and structure of highly relativistic MHD precessed jets. The simulation results reveal complex pressure structure inside the RMHD jet. The structure will be produced by a combination of the helical surface and body modes excited by the precession. The jet strongly interact with external wind. It means significant energy loss from the jet surface. To investigate the more detail of jet structure, we need theoretical works based on normal mode analysis. As future works we will plan to investigate the effect of external wind and in the regime of sub-magnetosonic relativistic jet flow. 1D Slices (parallel to the jet axis located at x/R j =0.12(solid line), 0.33(dashed line), 0.53(dashed-dotted line)) V t =0.01 case V t =0.1 case P gas BrBr BzBz vrvr vv wR j /v j Previous works for 3D relativistic hydro simulations (Hardee et al ) j / ext =10.0, v j =0.9165, v ext =0.0 adiabatic index =5/3, sound speed a ext =0.6121c, a j =0.2753c precessional perturbation with transverse velocity (v t =0.01c) and perturbation frequency (wR j /v j = 0.4, 0.93, 2.69) Axial velocities near the jet axis in slow transverse velocity case show that all of the simulations are in linear regime for initial transverse velocity (especially high-frequency case shows the classic linear exponential growth). In previous works of 3D hydro case (Hardee et al. 2002) the simulations are fully evolved out to about 30 R j for the low- and moderate-frequency. Therefore we need more longer simulations to check the simulations are fully evolved out. From comparison to 3D hydro case the simulation results show the similar tendency. However amplitude of velocities in 3D MHD case are much larger than 3D hydro case. It is because the effect of magnetic field and external wind. We need analytical works to investigate more detail. In fast transverse velocity case the simulations of middle- and high-frequency cases are fully evolved out and tend to non-linear regime. The radial magnetic field in meddle-frequency case shows substructure. It can be explained by the fluctuations in the axial velocity and pressure. The results of high-frequency cases with fast transverse velocity is very complicated. We suspect the simulations show the results of a beat frequency between helical surface and first body mode. It leads to the decrease in radial magnetic field and radial velocity. We need theoretical analysis to understand the complicated structure of these simulation results. 2D Plot (x-y plane, z/R j =15) of high-frequency case (wR j /v j =2.69) Vt=0.01 case Vt=0.1 case The jet interact with external wind. In fast transverse velocity case the pressure structure is more complicated and more strongly interact with external wind. It is because the simulation becomes non-linear phase. It expect significant energy loss from the jet surface. Schematic picture of Jet head region Simulation region P gas BrBr BzBz vrvr vv gzvzgzvz wR j /v j vrvr vv vzvz P gas z direction gzvzgzvz